Nutmeg-loving toucans wearing GPS transmitters recently helped a team of scientists at STRI address an age-old problem in plant ecology: Accurately estimating seed dispersal. The tracking data revealed what scientists have long suspected: toucans are excellent seed dispersers, particularly in the morning.
The researchers collected fresh seeds from a common Panamanian nutmeg tree and fed them to captive toucans at the Rotterdam Zoo. They gulp nutmeg seeds whole, the outer pulp is processed in the bird's crop, and the hard inner seed is then regurgitated. Five zoo toucans fed 100 nutmeg seeds took an average of 25.5 minutes to process and regurgitate the seeds.
In Panama, the scientists netted six wild toucans that were feeding from a large nutmeg tree in Gamboa. They fitted the birds with lightweight backpacks containing GPS tracking devices and accelerometers which can measure a bird's daily activity level. When matched with the seed-regurgitation time of the zoo toucans, the GPS data indicated the wild toucans were probably dropping nutmeg seeds a distance of 472 feet, on average, from the mother tree. Each seed had a 56% probability of being dropped at least 328 feet from its mother tree and an 18% chance of being dropped some 656 feet from the tree.
In addition, the accelerometer revealed that the toucans' peak activity and movement was in the morning followed by a lull at midday, a secondary activity peak in the afternoon, and complete inactivity at night. This is a normal pattern of tropical birds.
"Time of feeding had a strong influence on seed dispersal," the scientists write. "Seeds ingested in morning (breakfast) and afternoon (dinner) were more likely to achieve significant dispersal than seeds ingested mid-day (lunch)." This observation explains why tropical nutmegs are "early morning specialists" with fruits that typically ripen at early and mid-morning so they are quickly removed by birds. Ideally, the scientists observed, nutmeg trees could increase their seed dispersal distances by producing fruit with gut-processing times of around 60 minutes.
The article produced from this research was published by Kays et al, 2011. See citation under “New publications.” The article can be obtained from calderom@si.edu
http://www.stri.si.edu/english/about_stri/headline_news/news/article.php?id=1352
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